Imaging system including scintillation conversion screen

ABSTRACT

A portable, self-contained, electronic radioscopic imaging system uses a pulsed X-ray source, a remote X-ray sensor, and a self-contained, display and controller unit to produce, store, and/or display digital radioscopic images of an object under investigation in low voltage imaging environments such as medical applications including mammography and tissue imaging, and industrial radiography of low-density structures, or the like. The radiographic system uses an X-ray converter screen for converting impinging X-ray radiation to visible light, and thus each point impinged on the screen by X-ray radiation scintillates visible light emissions diverging from the screen. An image sensor, i.e., a CCD camera, is configured to sense the visible light from the screen. An aspheric objective lens operable with the CCD camera spatially senses visible light within a collection cone directed outwardly from the image sensor. An emission modification lens layer, e.g., a prismatic brightness enhancement film or a sprayed on transmissive layer, through which the visible light emitted from the screen is transmitted is superposed with the screen and positioned in an optical path between the aspheric lens and the screen for generally focusing the diverging visible light as a restricted cone of illumination propagating outwardly from each point impinged on the screen to increase the fraction of light directed into the collection cone of the first lens and reducing the amount of scattered visible light from the screen.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of application Ser.No. 09/225,885, filed Jan. 5, 1999, which is a continuation-in-part ofapplication Ser. No. 09/076,604, filed May 11, 1998, which is adivisional application of Ser. No. 08/773,483, filed Dec. 23, 1996, nowU.S. Pat. No. 5,828,726, which is a continuation of application Ser. No.08/494,251, filed Jun. 23, 1995, now U.S. Pat. No. 5,608,774.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a portable, self-contained,X-ray apparatus that digitally processes, displays, stores, and/ortransmits electronic radioscopic images of sealed packages, containers,or other objects, or of patients and animals, on location for security,customs, medical, and other non-destructive and non-invasive purposes.More particularly, the present invention relates to an enhanced X-rayconverter screen for use in X-ray radioscopic imaging systems whichincreases the detected brightness and reduces the effects of veilingglare and multiple reflections through the use of thin film lenslets orother light directing films or structures which simultaneously modifythe emission angle of light from the screen and change its reflectivecharacteristics to external light through the use of thin film lensletsor other light directing films or structures which simultaneously modifythe emission angle of light from the screen and change its reflectivecharacteristics to external light.

[0003] There are many instances in the medical, security or customsfield when it is necessary to examine or inspect, in a non-invasive way,a patient, animal, or other living organism; or to examine and inspect,in a non-destructive way, the contents of a closed package, box,suitcase, or other container. Some of the general concerns and problemsassociated with such examinations or inspections are set forth in U.S.Pat. No. 5,608,774, incorporated herein by reference.

[0004] Where the imaging system uses an objective lens coupled through acollection cone to a phosphor X-ray conversion screen, as is common inmany radioscopic imaging systems, there is a continuing need to improvethe brightness and contrast of the displayed image. This is because suchsystems are premised on the assumption that all of the emitted lightfrom the phosphor screen is collected into the collection cone of theobjective lens, thereby providing a clear, sharp image of the emittedlight. In practice, however, some of the emitted light is not collectedinto the collection cone and is scattered by objects within the imagerenclosure back onto a different portion of the phosphor screen, fromwhich location it is then diffusely reflected, with a fraction of thelight being sent back into the collection cone. Since this light appearsto originate from a differing point on the phosphor screen, iteffectively reduces the true contrast of the image.

[0005] Virtually all optical designs are plagued by the problem of lightoutside of the capture cone of the lens hitting other features withinthe optical system and being scattered back into the image. Generally,prior art designs attempt to solve this problem by making the walls ofthe system physically distant from the beam, using a series ofanti-scatter baffles just outside of the optical path, and coating allsurfaces with a very non reflective material. The literature containsdesigns for such systems as well as the formulations of paints andsurface treatments for accomplishing these goals.

[0006] Unfortunately, the above approaches are very difficult to use ina mirror folded system, such as is used for many X-ray imaging systems,including the present invention. Further, if one wants to restrict thedepth of the optical system (which is the case with the presentinvention) by using a mirror angle of 45 degrees or less, the problemsof containing the light emitted at angles that would normally not fallinto the collection cone and keeping this light from reflecting backonto the diffuse phosphor surface (where it may then bounce back intothe collected beam) becomes virtually impossible.

[0007] It is thus evident that improvements are needed within X-rayradioscopic imaging systems, as well as any imaging system that useslight emitted from a diffuse phosphor screen into the collection cone ofan objective lens, that both: (1) increase the fraction of light fromthe phosphor converter screen that is collected into the collection coneof the objective lens, and (2) which reduce the effects of light emittedfrom the diffuse phosphor screen not captured by the lens.

[0008] The present invention addresses the above and other needs.

SUMMARY OF THE INVENTION

[0009] The present invention enhances the optical portion, or “imager”,of an X-ray radiographic or similar optical imaging system by increasingthe fraction of light emitted from an X-ray converter screen that isdirected into the collection cone of an objective lens, while at thesame time reducing the effects of light emitted from the X-ray converterscreen (which comprises a diffuse phosphor screen) which leaves thescreen in a direction that is not captured by the lens. That is, theinvention reduces the amount of light that is permitted to scatterwithin the imager, and also suppresses any light that does scatterwithin the imager. By reducing the amount of scattered light, and bysuppressing what light does scatter, the collection cone of theobjective lens thus receives a greater portion of the emitted light, andthe optical system is thus able to produce a brighter image havingimproved contrast than has heretofore been achievable.

[0010] In accordance with one aspect of the invention, the amount oflight permitted to scatter within the imager is reduced by focusing morelight toward the center of the collecting lens through the use of thinlight directing films or structures.

[0011] In accordance with another aspect of the invention, the effectsof re-scattered light within the imager are suppressed, or minimized.

[0012] In general, one of three basic ways may be used to both intensifyon-axis light (focused light) captured by the lens and to reduce orsuppress off-axis light (scattered light). First, a baffle-likestructure or film that functions much like a venetian blind (sometimesreferred to herein as a “Chevron structure”) may be used to limit theangle of emission (and transmitted intensity) of the light that isdirected to the lens. Second, the light directed to the imaging lens maybe refocused with a sheet of tiny microlenses or one or more linearmicro prism structures adapted to collect a large fraction of the lightemitted below their collection surface area. Advantageously, suchrefocusing elements have a focal point very near the imaging screen'ssurface (thereby allowing the light to be highly focused); or, by properchoice of orientation, such refocusing elements may actually redirect analready restricted emission to incline its center more into thecollection cone and away from any other surfaces within the enclosure.Further, for that light which does scatter back from the walls of theenclosure, it may be made to strike specific reflecting surfaces ratherthan the diffuse surface of the screen so that the likelihood of thelight being scattered into the collection cone is reduced. Third,combinations of the first and second re-scattering reduction techniquesdescribed above may be used in a correlative manner so that theircombined effects add in a beneficial way to both reduce off axis lightas well as intensify the on-axis light captured by the lens.

[0013] In accordance with another aspect of the invention, appropriatelinear structures may be used along a single axis, providing enhancedoptical properties in one dimension, or crossed linear structures may beused along two axes, providing enhanced optical properties in twodimensions.

[0014] The invention is particularly applicable in situations where thelight from the conversion screen is limited. Such situations occur inlow voltage, X-ray imaging systems where the light emitted per X-rayphoton is weak due to the intrinsic low energy contained in theindividual X-rays. Primary applications of this type include, amongothers, medical applications, e.g., mammography and tissue imaging.Alternatively, one also finds the same situation in industrialradiography of low-density structures such as composite materials. Atthe other extreme are cases in which the X-ray conversion screen (whichconverts X-ray energy to light), has been chosen to be of a very highdensity to provide good interaction efficiency but where the phosphordoes not convert the energy to light with great efficiency. In eithercase, one of the aspects of the present invention is directed toimproving the amount of light captured from the screen into an opticalsystem and subsequent imager. The light collection may be a function of(1) the initial X-ray energy flux, (2) the probability of interactionwithin the screen, (3) the energy to light efficiency, or (4) theoptical collection efficiency of the lens or other optical system. Thedescribed embodiment is directed particularly to improving lightcollection by way of the last term in the equation, i.e., the opticalcollection efficiency.

[0015] Since the goal of a good imaging system is to bring down allsources of noise to a level below one X-ray photon, it is important thateach X-ray event produce the highest detectable light output possible.This is the primary of effect of the enhanced X-ray converter screen forradioscopic systems described herein. The additional benefit is that theinternal scattering of light within the imager enclosure issignificantly reduced which also benefits the image quality by extendingthe range of penetration into the darker portions of the image.

[0016] It is thus an object of the invention to employ light-directingfilms or Chevron-like structures within the optical portion of an X-rayradiographic or similar optical imaging system that provide simplemasking of emission angles so as to better direct the reflected lightinto the collection cone.

[0017] It is another object of the invention to provide light-directingstructures within the optical portion of an X-ray radiographic orsimilar optical imaging system that use the refractive power of an arrayof lenslets or linear microprisms.

[0018] It is yet another object of the invention to provide an X-rayconverter screen and a method of converting X-ray radiation to visiblelight.

[0019] It is a further object of the present invention to provide aradiographic system employing an objective lens in which a visible lightemission modification layer is superposed with an X-ray converter screenfor generally focusing the diverging visible light as a restricted coneof illumination propagating outwardly from each point impinged on thescreen to increase the fraction of light directed into the collectioncone of the objective lens while reducing the amount of scatteredvisible light from the screen.

[0020] An advantage provided by the invention is that suchlight-directing films or structures effectively concentrate the emissionangle of the normal lambertian pattern and redirect the centroid of thatangular distribution toward the center of the collecting lens, therebyproviding an enhanced image for the imaging system. In effect, thisapproach trades off an increase in brightness and reduction in off axisemission for the spatial quantification of the totality of light emittedfrom under each lenslet, microprism or other structure.

[0021] In a described embodiment, a radiographic system uses an X-rayconverter screen for converting impinging X-ray radiation to visiblelight, and thus each point impinged on the screen by X-ray radiationscintillates visible light emissions diverging from the screen. An CCDcamera image sensor is configured to sense the visible light from thescreen. An aspheric objective lens operable with the CCD cameraspatially senses visible light within a collection cone directedoutwardly from the image sensor. An emission modification lens layer maybe provided as a prismatic brightness enhancement film, through whichthe visible light emitted from the screen is transmitted is superposedwith the screen and positioned in an optical path between the asphericlens and the screen.

[0022] Briefly summarized, the present invention relates to aradiographic system and an X-ray converter screen including a substratefor converting impinging X-ray radiation to visible light, each pointimpinged on the substrate by X-ray radiation scintillating visible lightemissions diverging from the substrate. An emission modification layerthrough which the visible light emitted from the substrate istransmitted generally limiting the diverging visible light to arestricted cone of illumination propagating outwardly from each pointimpinged on the substrate by the X-ray radiation. The invention furtherrelates to a method of converting X-ray radiation to visible light byproviding an X-ray converting screen, and then superposing the screenwith a transmissive film for modifying the transmission of visible lightemitted from the screen to generally limit the diverging visible lightto a restricted cone of illumination propagating outwardly from eachpoint impinged on the screen by the X-ray radiation.

[0023] From an imaging system point of view, and with particularreference to the disclosure provided in the '774 patent, a goal of thepresent invention is to use the enhanced optical system herein describedwithin a completely digital imaging system capable of recording anddigitizing the individual X-ray image data, including the ability tostore and retrieve that data onto a suitable storage medium, such as ahard disk of a portable computer. Such portable computer may then serveas a controller for selectively displaying the image in a way thatreveals the full dynamic range and resolution of the sensor. Inaddition, the image captured by the system may be transmitted to remotelocations (when necessary) via a modem for evaluation by experts who arenot on site.

[0024] The above and other goals are met by providing a portable,self-contained, electronic radioscopic imaging system. Such systemtypically includes three main subsystems: (1) an X-ray source, (2) aremote X-ray sensor, or “imager”, and (3) a self-contained, display andcontroller unit, or “display/control unit.” The X-ray source emitsX-rays at the object being investigated. The X-ray sensor or imagerutilizes a scintillating screen that produces flashes of light whenimpinged by an X-ray in combination with either an integrating CCDcamera, or an active matrix of thin film transistors and thin filmsample-and-hold photodiodes, to produce an integrated signal thatrepresents the sum of the radiation that pass through the object in agiven pixel area. Advantageously, the light directing films orstructures described herein, when used within the imager, produce animage exhibiting more brightness and better contrast than has heretoforebeen available in an imaging system of this kind. The self-containeddisplay and control unit utilizes digital signal processing within anenhanced portable computer, including a solid-state flat panel displayand associated drive circuitry, in order to display to an operator thefull dynamic range and resolution of an image-capturing sensor utilizedwithin the imager. A modem further permits the digitized image to besent to a remote location where the exact same image can be recreatedfor analysis by off-site experts.

[0025] Other features of the imaging system may be the same as, orsubstantially similar to, those described in the '774 Polichar et al.patent, previously incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other aspects, features and advantages of thepresent invention will be more apparent from the following moreparticular description thereof, presented in conjunction with thefollowing drawings wherein:

[0027]FIG. 1 depicts an imaging system in accordance with the presentinvention as it is used to form a radiographic image of a package underinvestigation;

[0028]FIG. 2 is a block diagram of the imaging system;

[0029]FIG. 3A illustrates a CCD camera version of the X-ray sensor usedwith some embodiments of the system of FIGS. 1 and 2;

[0030]FIG. 3B depicts a TFT flat panel amorphous silicon X-ray sensorused with other embodiments of the system of FIGS. 1 and 2;

[0031]FIG. 4 is a block diagram of the imaging system and showsadditional detail of the display/controller unit;

[0032]FIG. 5 is a perspective view of a special shield that is used toshield the CCD camera included in FIG. 3A;

[0033]FIG. 6 is a schematic diagram of the panel driver circuitry ofFIG. 4;

[0034]FIG. 7 depicts the various software modules that may be invoked bya user of the imaging system of FIGS. 1 and 2;

[0035]FIGS. 8A, 8B and 8C respectively depict various windows or“screens” that are displayed to a user as different control options areselected;

[0036]FIG. 9 graphically illustrates the manner in which the presentinvention achieves contrast stretching.

[0037]FIG. 10 illustrates the basic emission of light from a diffusephosphor screen without transmissive films as is employed in theembodiment of FIG. 3A;

[0038]FIG. 11 illustrates a radiographic system utilizing a transmissivefilm emission modification device such as a microlens film in accordancewith the present invention;

[0039]FIG. 12A shows linear prismatic superposed with an X-rayconverting screen, and FIG. 12B shows a layer of sprayed micro-spheresfor concentrating the emission light cone from the scintillation screenshows as employed in the radiographic system of FIG. 11;

[0040]FIG. 13 illustrates transmissive film having a multiplicity ofslats which restrict the transmission of light to emissions directed bythe orientation of the slats;

[0041]FIG. 14 is a radiographic system showing microlens film focusingthe diverging visible light as restricted cones of illuminationpropagating towards the collection cone of the objective lens inaccordance with an additional embodiment of the present invention;

[0042]FIG. 15 depicts the operation of transmissive film in the form ofmultiple corrective microlenses for directing light emissions; and

[0043]FIG. 16 shows a prismatic film having corrective microlenses orprisms in two dimensions.

[0044] Corresponding reference characters indicate correspondingcomponents throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0045] The following description is of the best mode presentlycontemplated for carrying out the invention. This description is not tobe taken in a limiting sense, but is made merely for the purpose ofdescribing the general principles of the invention. The scope of theinvention should be determined with reference to the claims.

[0046] Turning first to FIG. 1, there is shown an imaging system 10 madein accordance with the present invention. The system 10 includes threemain subsystems: (1) a portable X-ray source 12, (2) an imager 14, and(3) a Display/Control Unit 16. The three subsystems are interconnectedwith two cables. A first cable 18 is a “long” cable and is connectedbetween the Display/Control unit 16 and the imager 14. The long cablemay be as long as 180 feet. A second cable 20 is a “short” cable that isconnected between the imager 14 and the X-ray source 12. The short cableis typically less than 10 feet in length.

[0047] Advantageously, the system 10 is portable, which means it issufficiently lightweight and non-bulky to enable a single person tohand-carry its three constituent subsystems and associated cables to afield location where an object 22 to be investigated is located. Once onsite, the system 10 is designed to: (1) facilitate quick and easy setuparound the object 22 to be investigated, (2) provide rapid imageacquisition at the field location, and (3) provide image enhancementtools that aid in the evaluation of the acquired image.

[0048] In operation, the system 10 is setup by placing imager 14 next tothe object 22 to be investigated, e.g., as close as possible to theobject. The X-ray source 12 is then placed, e.g., two to three feet fromthe imager 14, on the opposite side of the object 22. Thedisplay/control unit 16 is then connected to the imager by way of thelong cable 18 and is placed a safe distance from the object 22. TheX-ray source is also connected to the imager 14 by way of the shortcable 20. When everything is properly connected, all three subsystemsare turned on, and under control of the display/control unit 16, theX-ray source 12 generates a pulsed X-ray beam (represented by the lines23) that is allowed to pass through the object 22. The pulsed X-rayspass through respective segments of the object 22 with varying degreesof intensity, or energy, as a function of the contents of the object 22,and are captured or sensed at corresponding pixel areas of the imager14. The intensity or energy of these pulses that pass through the object22 are accumulated or summed (integrated) over the duration of thepulsed beam (exposure time), which exposure time may include, e.g., aburst of 15-99 pulses.

[0049] At the conclusion or termination of the pulsed beam, the imager14 has acquired an integrated or summed energy for each pixel of thedisplay area, with the combined collection of all such energies for allthe pixels comprising an integrated image signal. The integrated imagesignal is then transferred to the display/control unit where it isappropriately processed and displayed. Such processing includesdigitizing the signal to facilitate its subsequent storage, retrieval,enhancement, display and/or transmission.

[0050] Advantageously, the system 10 is designed for safety and ease ofoperation. X-ray safety is assured, e.g., through the use of the pulsedX-ray source 12. Such pulsed source produces extremely short bursts ofX-rays capable of penetrating several inches of most materials, yetgenerates extremely low radiation dose (integrated exposure) levelsoutside the direct source beam. Safety is further enhanced by twointerlock keys, both of which must be in place and in the “ON” positionin order for the X-ray source 12 to be activated. A first interlock key24 is at the display/control unit 16. A second interlock key 26 is atthe X-ray source 12. Moreover, a software interlock is provided as partof the operation of the display/control unit 16. Such software interlockgenerates and displays a warning message on a screen 28 on thedisplay/control unit 16 and then requires the operator to acknowledgesuch warning message by pressing a key on a keyboard 30 of thedisplay/control unit 16 before the X-ray source can be triggered.

[0051] An additional safety feature is provided through the use of thelong cable 18 which permits the display/control unit 16 (and hence theoperator) to be located a safe distance (the length of the cable 18)from the object 22 being investigated. The cable 18, for example, may beas long as 180 feet, although in the preferred embodiment it is onlyabout 60 feet (typically provided through two 30-foot sections). Thecable 18 could be made even longer, if desired, if appropriate linedrivers are inserted into the line at regular intervals, and/or if adifferent transmission medium is used (e.g., fiber optic cable, and orRF wireless transmission).

[0052] Turning next to FIG. 2, there is shown another diagram of theimaging system 10 which illustrates, in block diagram form, essentiallythe same elements as are depicted in FIG. 1. However, FIG. 2 showsfurther detail of the display/control unit 16 (which hereafter may bereferred to as simply the “control unit 16”), and in particular showsthat the control unit 16 includes a computerized digitizer and imageprocessor 32, a solid state display panel 28, a keyboard and operatorpointing device 30, removable digital media 34, and a modem 36 to allowconnection to a phone line 38. The long cable 18 connects between thecomputerized digitizer and image processor 32 and the imager 14(sometimes referred to herein as an “X-ray sensor”). The signals sentand received over the long cable 18 include the integrated image signaland a trigger signal, as well as an operating voltage (power) for theimager 14. The trigger signal triggers both the integration circuitrywithin the imager 14 as well as the X-ray fire line going to the pulsedX-ray source via the short cable 20.

[0053] Advantageously, the pulsed X-ray source 12 may be realized usingany suitable commercially available X-ray source. One commerciallyavailable X-ray source that may be used within the system 10, forexample, is the Golden Inspector® Model 200 X-ray source manufactured byGolden Engineering Inc., P.O. Box 175, Centerville, Ind., 47330, theoperator's manual for which is incorporated herein by reference. TheInspector Model 200 X-ray source has a maximum output energy of 150 kV,and produces about 3.0 mRem output dose per pulse at one foot (on thebeam centerline, with 2.5 mm aluminum filter). It includes a built-inelectronic counter to provide from 0-99 pulses. The X-ray pulses thatare generated have a nominal pulse width of 50 nanoseconds. The nominalpulse rate is 20-25 pulses per second (pps). It is a modular designhaving approximate dimensions of 4.2 inches wide by 4.2 inches deep by15 inches long. It weighs only 20.5 pounds with a battery. It alsoincludes a standard camera tripod mounting plate (¼-20 thread). Besidesa battery, it includes a power cord and self-contained 29 voltrechargeable battery pack. The source 12 may be battery operated or itmay be plugged into a 110/220 VAC, 50/60 Hz power outlet usingconventional power cords. Switching between battery and line power isautomatic. Other equivalent portable X-ray sources could, of course, beused in lieu of the Golden Inspector Model 200 X-ray source.

[0054] The X-ray source 12 should be positioned so that the beamcenterline intercepts the “imager screen” near its center. The imagerscreen is that portion of the imager 14 designed to be impinged by thepulsed X-rays that pass through the object 22, and hence that portion ofthe imager which captures the X-ray image. One of the advantages ofusing the modular X-ray source 12 is that it can be readily adjusted inheight and orientation by positioning it on the floor, on risers, or onan adjustable platform, as required. The imager 14 may also be adjusted,as required, so that the region of interest of the object 22 is as closeas possible to the imager screen. The location of the imager screen onthe imager 14 may be denoted by a rectangular indentation on the face ofthe imager 14, or by other suitable markings (e.g., painted lines). TheX-ray source is preferably positioned approximately two to three feetfrom the imager screen for best image results.

[0055] It is also preferred that a suitable X-ray source beam filter 13(FIG. 2) be used with the X-ray source 12 in order to enhance thequality (resolution and contrast) of the resulting image. An X-rayfilter typically comprises a thin metal sheet that is placed over theexit aperture of the X-ray source to remove by absorption and scatter afraction of the low energy X-rays. It has been found that, depending onthe thickness and material composition of the object imaged, very lowenergy X-rays in the source beam may not be contributing to theformation of the X-ray image formed (which X-ray image is, in essence,an X-ray “shadow” of the object(s) placed in the path of the X-ray beam)by transmission through the object. These low energy X-rays, however,are believed, in some instances, to decrease the quality of the image bycontributing to statistical noise, thereby resulting in a decrease inimage resolution and contrast through scattering. Hence, the filter 13is used to remove such low energy X-rays. The type and thickness of thefilter 13 to be used typically depends on the thickness and compositionof the object.

[0056] When imaging a thin, or lightweight target, the filter 13 shouldbe of minimal thickness, such as 0.005 to 0.010 inch thick copper or0.020 to 0.030 inch thick aluminum. If the target 22 contains densematerials, a more substantial filter 13 may give better results. Acopper filter of 0.020 inch thickness may help image effectively steelobjects. Alternatively, use of a 0.050 inch thick aluminum filter isalso believed to produce satisfactory results.

[0057] The problem of imager saturation, sometimes referred to as“blooming”, can be corrected by decreasing the exposure time. It hasalso been learned that imager saturation can be lessened using asuitable beam filter 13. When trying to image objects which haveadjacent areas of high and low density materials, saturation of the lessdense regions can hide detail in the dense areas. By employing thedifferent thicknesses of filtering materials, it has been found possibleto reduce or even eliminate this “blooming” problem, reduce noise due toscattering, and produce a more detailed radioscopic image.

[0058] The imager 14 is realized by application of a suitable X-raysensor. One type of X-ray sensor that may be used for the imager 14, forexample, is an integrating CCD camera subsystem 14′ modified inaccordance with the present invention, as shown in FIG. 3A. As seen inFIG. 3A, the CCD subsystem 14′ includes a lightweight metal housing 40,e.g., made from 0.06 inch thick aluminum, that holds an X-ray lightconverter screen 42, which screen 42 functions as the “imager screen”referred to above. Typically, the screen 42 is eight by ten inches insize, and is realized using a suitable scintillating screen, e.g., aphosphor scintillating screen. As the X-rays strike a particular pixelarea of the scintillating screen 42, flashes of fluorescence occurhaving an intensity or energy proportional to the energy of the X-raybeam. Such flashes are then optically guided through a suitable opticalpath, which includes a front surface mirror 44, through a fast lens 46,to a solid-state, compact, integrating charge-coupled device (CCD)camera 48.

[0059] The image is recorded within the CCD camera 48, and is convertedto a standard video signal that is sent to the control unit 16 via thelong cable 18 (FIGS. 1 and 2), The housing 40, in the preferredembodiment of the imager 14′, includes a built-in handle to helptransport it. Such handle may also be positioned to help hold or supportthe housing so that the screen may be maintained in a generally verticalposition when the imager 14′ is oriented as shown in FIG. 3A.

[0060] A preferred imager 14′ has approximate dimensions of 10.3 incheswide by 12 inches high and 7 inches deep. The weight of the imager 14′is under 10 pounds. Operating power for the imager 14′ is obtainedthrough the cable 18 from the control unit 16, and is typically providedby way of a power supply voltage of 12 volts. Hence, like the othercomponents of the overall system 10, the imager 14′ is readily portableand easy to use at an on-site field location.

[0061] As indicated previously, the CCD camera 48 integrates the imageover a prescribed number of X-ray pulses (exposure time).Advantageously, the integration of the light image (resulting from theflashes of fluorescence that occur as the X-ray pulses impinge thescintillating screen) occurs on the CCD chip, as opposed to beingcarried out using off-chip electronic circuitry. The normal chargereadout is inhibited during the integration period, thereby making suchcharge readout available at the completion of the integration period foruse as the standard video signal, or integrated signal, previouslyreferenced. Further, integration only occurs in synchrony with thegeneration of the burst of X-ray pulses, thereby effectively blockingout “noise” that is present at times other than when the X-ray burst ispresent.

[0062] In the preferred embodiment of the imager 14′, the CCD camera 48is realized using an 1100 Series Board Level Monochrome CCD Cameraobtained from Cohu, Inc. 5755 Kearny Villa Rd., San Diego, Calif.,92123. The 1100 Series CCD cameras feature a ½ inch-format on-chipmicrolens sensor, mounted to an electronic board whereon supportingelectronic circuitry is placed, such as driver circuits, videogeneration circuits, power supplies, and the like. Advantageously, the1100 Series cameras may readily be configured for custom purposes. Inthis instance, the only significant modification that needs to be madeto the 1100 Series CCD Camera obtained from Cohu is to change theintegration time of the camera from being controlled by a start/stoppulse, to being controlled by an exposure time (number of pulses) sothat integration occurs only during the pulsed X-ray burst, and not atother times. Even this modification would not be required is one choseto generate a separate start/stop pulse coincident with the beginningand ending of the exposure time. However, by making the modificationindicated above, the need for such a separate start/stop pulse iseliminated, thereby reducing the number of signals that need to becommunicated through the long cable 18.

[0063] With a Series 1100 CCD camera (or equivalent camera where amicrolens sensor is mounted on an electronic board), it has been foundthat the CCD camera 48 needs to be protected from exposure to ionizingradiation damage. Two types of problems may arise. First, X-rays whichpenetrate the imager 14′ without interacting with the scintillatingscreen 42 may strike the CCD chip of the camera 48. If this happens,visible specks of white light appear on the image, thus reducing theimage quality. Second, prolonged exposure to such radiation can prove tobe harmful to the integrated circuit components, e.g., the CCD chip orother integrated circuits used to generate the video signal, possiblyresulting in failure of such circuits.

[0064] In order to reduce the number of X-rays that strike the camera48, the camera 48 is encased in a 0.125 inch thick lead housing orshield 50. The preferred shield 50, for use with the particular CCDcamera 48 specified above, is shown in its folded state in FIG. 5,before placing it around the CCD camera 48. In addition, a 0.25 inchthick lead plate 52 may be placed between the CCD-chip and incidentX-ray radiation in order to further shield the CCD chip from strayX-rays.

[0065] A further aspect of the invention concerns the use of the firstsurface of the mirror 44 (FIG. 3A) to direct the image of thescintillating screen 42 to the CCD camera 48. Employing the mirror 44 asshown, i.e., in line with the X-rays that strike the scintillatingscreen, permits placement of the CCD camera 48 at a location outside ofthe main X-ray path, thereby significantly reducing the number of X-raysthat might otherwise directly strike the CCD camera or its associatedelectronic components. (Note, any the X-rays that pass through thescintillating screen 42 would also pass through the mirror 44.)

[0066] As indicated, the preferred CCD camera 48 is an 1100 Series CCDcamera made by Cohu of San Diego, Calif. Representative specificationsof the Cohu's 1100 Series camera are as follows: Pick Up Device: ½″Interline transfer, microlens sensor Active Picture RS-170: 768 (H) ×494 (V) Elements: CCIR: 752 (H) × 582 (V) Pixel Cell Size: 8.4 μm (H) ×9.8 μm (V) Total Pixel Elements: 811 (H) × 508 (V) Resolution: RS-170:  580 horizontal TVL, ≧350 vertical TVL Synchronization Horizontal andVertical Crystal (RS-170) Asynchronous reset Shutter {fraction (1/60)}to {fraction (1/10000)} Power 12 VDC, 3.6 W max Size 1.75 × 3.88 × 1.00inches

[0067] Another type of X-ray sensor that may be used as the imager 14 isa flat panel sensor 14″, as shown in FIG. 3B. Such sensor 14″ offers theadvantage of being flat and relatively thin so that it can be positionedinto tight spots, and further eliminates the need for a mirror(s) and/orlenses to define an optical path. The sensor 14″ includes a conventionalX-ray scintillation screen 42′ that is in direct contact with a flatpanel, amorphous silicon, TFT (thin film transistor) photo sensor 52.The TFT photo sensor 52 is made on a glass or ceramic substrate 54, andincludes a matrix of thin film transistors 60. Each TFT further has itsown thin film sample and hold (S&H) photodiode 62 associated therewith.The matrix of TFT's and S&H diodes is sufficiently dense so that eachTFT 60 and associated S&H photodiode 62 corresponds to a different pixelof the sensor 14″. The S&H photodiode 62 senses and accumulates all ofthe light flashes produced at the corresponding pixel of thescintillation screen 42′ during the integration time. At the end of theintegration time, the accumulated signal at each pixel site that is heldby the corresponding S&H photodiode 62 is read through its correspondingTFT transistor 60 through appropriate row drive electronics 56 andcolumn drive electronics 58, in conventional manner. Such accumulatedsignals, for all of the pixels of the sensor 14″, thus comprise theintegrated image signal for a given exposure time.

[0068] Further details of the manner of making and using a flat panelsensor of the type illustrated in FIG. 3B as the sensor 14″ aredescribed, e.g., in Street, et al., “Amorphous Silicon Arrays Develop aMedical Image,” IEEE Circuits and Devices, pp. 38-42 (July 1993); and Wuet al., “Imaging With Page-Sized A-Si:H 2-Dimensional Sensor Arrays,”SPIE Proceedings, Vol 2172 pp. 144-154. Both of these references areincorporated herein by reference.

[0069] Turning next to FIG. 4, a more detailed block diagram of theimaging system 10, and particularly of the control unit 16, isillustrated. As seen in FIG. 4, at the heart of the control unit 16 is asingle board computer (SBC) 70. The SBC 70 is connected in conventionalmanner to a PCMCIA port 72 (adapted to interface with a removable harddisk 34), a hard disk 74, a floppy disk drive 76, a keyboard/pointer 30,and a modem 36, all of which are of conventional design. The SBC 70further interfaces, through a suitable bus 78, with digital controlcircuitry 80 (for generating-/interfacing the digital control signalsthat are sent to the imager 14 and the X-ray source 12), a videographics adapter 82 and an image digitizer and display memory 84, all ofwhich may also be of conventional design, except as indicated below. Theimage digitizer and display memory 84 further interfaces, through paneldriver circuitry 86, with an active matrix monochrome display panel 28.Advantageously, all of the components of the control unit 16 areeffectively those of a conventional personal computer (PC), with somemodifications, as explained below.

[0070] While any suitable PC could be used and modified for use with theinvention, the preferred PC is at a minimum a 486 class microprocessor,or better, operating at a preferred minimum clock speed of about 33 MHZ,and modified as required to drive the active matrix monochrome displaypanel 28 so that it exhibits a large gray scale resolution, e.g., a grayscale that provides 256 different shades of gray. Such gray scaleresolution is generally not commercially available, to applicant'sknowledge, particularly in a small, transportable, ruggedized,self-contained, has-the-appearance-of-a-suitcase, unit. When modified,as explained below, the unit 16 has dimensions of only 18 by 13 by 7inches, weighs only about 24 pounds (including a battery pack), and ishoused in a “suitcase” housing that, when closed, does not readilyidentify its function. Such disguised appearance can be an importantfeature for some applications of the invention so that the unit can beeasily carried into a desired field location, e.g., a busy airportterminal, without initially drawing undue attention thereto.

[0071] As indicated, most of the components of the control unit 16 areconventional components that may be provided by any suitable computermanufacturer. The principal exception to this general availability isthe active matrix display 28 and associated driver 86. The use of a flatpanel display 28 is very desirable for a portable system from aportability and ruggedness perspective. Advantageously, the use of a TFTflat panel display is particularly suited for the imaging system 10because of the available brightness and wide range of available colorsand grayscales. Disadvantageously, the use of TFT flat panel devices iscomplicated by the fact that they are relative recent additions to thedisplay market, and the interface electronics to drive these displays,particularly for a monochrome application where a high grayscaleresolution, e.g., 256, is desired, is not yet available. To furthercomplicate matters, the signal to be displayed for the imaging system 10is an analog VGA video signal, rather than a digital drive signal as iscustomarily used to drive such displays.

[0072] In view of the above difficulties, the present invention uses acustom panel driver circuit as shown in FIG. 6. The circuit in FIG. 6,explained more fully below, performs the function of converting thestandard VGA signal, with its three component signals, red (R), green(G), and blue (B), to a digital signal suitable for driving the TFTactive matrix flat panel display 28.

[0073] The preferred active matrix flat panel display for use with thecontrol unit 16, but certainly not the only flat panel display thatcould be used, is a LDH096T-11 display made by Flat Panel Display Co. ofEindhoven, The Netherlands. The LDH096T-11 is a 9.5 inch diagonal LCDmodule that comprises an Active Matrix Liquid Crystal Display, anintegrated adjustable backlight and module electronics. The moduleelectronics facilitate interfacing with commercially-available VGAchipsets, and can display either 16 or 256 levels of gray depending onuser selection. The display resolution of the LDH096T-11 is 640 by 480dots, with a dot pitch of 300×300 μm. The contrast ratio is better than60:1 at optimum viewing angles, and the brightness is 60 cd/m². Theactive area of the display is 192 by 144 mm. The power consumption,including backlight, is only about 2.5 Watts (nominal). The supplyvoltage for the display is 5 volts.

[0074] The panel driver circuit used to drive the LDH096T-11 display isshown in the schematic diagram of FIG. 6. The main signal inputs to thecircuit shown in FIG. 6 comprise the RGB signals from the analog VGAsignal, which signals are applied to connector J2 and directed toamplifier/summer U3, where they are multiplied by an appropriate gainfactor and summed. The summing of the three RGB signals combines thesignals, putting them on a single signal line (the output of amplifierU3). This summed/combined signal is then applied to analog-to-digital(A/D) converter U4, which converts the signal to an appropriate digitalsignal that can be applied to the display 28 through connector J3. Thenecessary clock signals and control signals needed by the A/D converterU4 and the flap panel display via connector J3 are generated in theprogrammable array logic contained in device U1. Other components, aswell as control, timing and voltage signals, used within the circuitshown in FIG. 6 should be self-evident from the schematic diagram ofFIG. 6 to those skilled in the electronic arts.

[0075] A preferred control unit 16 for use with the present inventioncomprises a modified SafeCase® Series 4000 Rugged Portable Computer madeby Industrial Data Systems, Inc., 14900 Woodham Drive, Building 170,Houston, Tex. 77078-6016. The Series 4000 computer is ordered to includean 80486 microprocessor with a clock speed of 33 MHZ, 8 MB of RAM, a3.5″ high density floppy disk drive, and at least a 210 MB hard drive.The basic unit offered by Industrial Data Systems (IDS) as specifiedabove is further modified for 120/220 VAC 50/60 Hz/12 VDC operation,including a battery charger that charges the battery automaticallywhenever the unit is connected to a 120/220 VAC power line. To enhancebattery operation, a Microbus MAT 752 low power 486DX/33 CPU board isinstalled in the unit 16 as the SBC 70. With such low power CPU board, afully charged battery pack permits 75 to 80 minutes of operation of theunit. The charge level of a given battery pack can be tested at any timeusing a built-in push button and LED display located at the lower rightcorner of the battery pack. The battery packs may also be chargedexternal to the unit 16 using a suitable battery pack charger.

[0076] As additional modifications to the Series 4000 Portable Computer,an Interlink Durapoint mouse pad pointing device, or other pointingapparatus, is built into the top panel the case (or otherwise madeavailable to the user). Preferably, such pointing apparatus ispositioned to be centered just below the keyboard so that a user canmanipulate it with his/her thumbs while keeping his/her fingers on thekeyboard. A PCMCIA Type III connector is also added to the top panel,and the Microbus CPU Board is connected to drive this port. It isthrough this port that removable storage media, or other peripherals,may be connected to the Microbus CPU Board. In addition, the I/O(input/output) expansion plate of the unit is punched to accept anAmphenol #165-159236 connector and cable, which when installed andconnected to the Microbus CPU Board, functions as the connector for thelong cable 18. The LCD panel is modified to accept the above-describedFPD LDH096T-11 display 28, and the panel driver circuitry 86 (shown inFIG. 6) is appropriately installed within the unit 16 so as to drive thedisplay 28 as controlled by the Microbus CPU board. Also installed inthe unit 16 is an internal modem and external RJ-11 jack to facilitatemodem communications.

[0077] The image digitizer and display memory 84 (sometimes referred toherein as simply the “image processor” 84) comprises a separate orauxiliary processor installed within the control unit 16 in order tofacilitate the receipt, processing, and display of the integrated signalfrom the imager 14. Such image processor 84 may take several forms, andthere are numerous commercially- available processor boards that couldbe used for this purpose. At the present time, one of two commerciallyavailable processors is preferred for use as the image processor 84,both of which are manufactured and sold by Matrox Electronic Systems,Ltd., 1055 St. Regis Blvd. Dorval, Quebec, Canada H9P 2T4. A firstpreferred processor is the Matrox Image-LC image processor, which isdesigned to interface with a wide range of analog and digital devices.The Matrox Image-LC processor, the operator's manual for which isincorporated herein by reference, is a programmable processor that isvery versatile, and provides a great many options, such as the abilityto perform mathematical computations on a pixel by pixel basis at theprocessor 84 (as opposed to being performed at the SBC 70). The resultis very fast image processing. Because the Image-LC processor is a verycapable and fast processor, it is also somewhat expensive and consumes asignificant amount of power.

[0078] A second preferred processor for use as the image processor 84 isthe Matrox IP-8 Frame Grabber. The Matrox IP-8 Frame Grabber, theoperator's manual for which is also incorporated herein by reference, isa flexible, low-cost monochrome frame grabber and display processor thatoffers only a few of the processing features of the Image-LC processor.However, the IP-processor still offers sufficient processing capabilityfor most applications of the present invention. For this reason, andgiven its lower-cost, and less power consumption, the IP-8 Frame Grabberis the image processor that is generally used most often with thepresent invention.

[0079] The Video Graphics Adapter (VGA) 82 of the control unit 16comprises a standard VGA board, as is used in any personal computerproviding VGA graphics.

[0080] The digital controller 80 of the control unit 16 functions toprovide an appropriate isolated interface between the control unit 16and the imager 14 and X-ray source 12 relative to the trigger orsynchronization signals that must be sent to the imager 14 and X-raysource 12. More particularly, for the preferred X-ray source 12 andimager 14 described above, the controller 80 produces a TTL(transistor-transistor logic) electronic synchronization signal whichwhen driven to a ground potential accomplishes both (1) the firing ofthe X-ray source 12, and (2) the integration of the image signal at eachpixel site within the imager 14. When the TTL signal is returned to +5VDC, the X-ray source is inhibited, and the integrated signal is readout of the imager 14 after the next video vertical interrupt. The netresult (and desired goal) is that the rapid read out of the video signalfrom the imager 14 is properly synchronized with the digitizer of theimage processor 84. As seen in FIGS. 1, 2 and 4, the X-ray source 12 isconnected to the control unit 16 through the imager 14. That is, thelong cable 18 is connected between the control unit 16 and the imager14, and the short cable 20 is connected between the imager 14 and theX-ray source 12, and there is not direct cable connection between thecontrol unit 16 and the X-ray source 12. An isolation relay is used atthe imager 14 to apply a trigger (or “fire”) signal to the X-ray source12 through the short cable 20 as soon as the TTL synchronization signalis pulled low (or no longer than one frame time thereafter, where oneframe time is, e.g., the vertical blank interrupt period, typically{fraction (1/60)} of a second). The X-ray source continues generatingits burst of X-ray pulses until the TTL signal goes high (or until nolonger than one frame time after the TTL returns to +5 VDC).Advantageously, use of the isolation relay keeps electrical noise fromgetting into the video signal or affecting the stored image on the CCDchip. Thus, it is seen that the imager 14 is enabled (its “shutter” isopen to receive an image) at the same time as, or perhaps even justslightly before, the X-ray source 12 provides its burst of X-ray pulses,and remains enabled for so long as, or perhaps even just slightly longerthan, the burst of X-ray pulses ends. After completion of the exposure,i.e., within one frame time thereafter, the integrated signal acquiredat the imager 14 is downloaded to the image processor 84, and isthereafter available for display at the active matrix display 28 and/orfor storage within any of the available storage media used by thecontrol unit 16.

[0081] Advantageously, because the control unit 16 is based on a PC-typedigital computer, and because of the conventional components used withinsuch computer, both in terms of hardware and software, it is capable ofaccomplishing a wide variety of image acquisition, manipulation and datastorage tasks. Many of these tasks may take advantage of recent advancesin Graphical User Interface (GUI) technology, particularly in view ofthe fact that the familiar MICROSOFT (MS) Windows operating system isbeing used. For example, with hardware which supports “DigitalChromokeying”, it is possible to superimpose images stored in the memoryof the image acquisition memory buffer with the MS Windows desktopdisplay. Such capability provides a very compact and convenient userinterface.

[0082] Further, because PC-based technology is used within the controlunit 16, there exists great flexibility in how the resulting data isstored and transmitted. For example, the conventional TIF binary fileformat, commonly used for faxes, drawings, and other graphical(digitized) displays/images in the PC-based environment, may be used tostore and manage the digitized images. Fortunately, a significant bodyof commercially-available software exists to aid in the handling,storage, and management of such displays. In addition, such TIF imagescan be copied to a standard 1.44 MB floppy diskette, using the floppydisk drive included as part of the control unit 16, or to a standardremovable hard drive (which has the capacity to store hundreds of suchimages) using the PCMCIA port, or transmitted via the modem 36. As aresult, the images can be transported, transferred and/or copied ontoany other PC compatible system. Such images can then be viewed,manipulated, and/or printed using one of the numerous graphics anddesktop imaging programs which are commercially available.

[0083] The control unit 16 stores the digital image in a frame buffermemory that forms part of the image processor 84 (FIG. 4). Such storageof the image allows the host computer, i.e., the SBC 70, and/or theimage processor 84 (if the image processor has such capability) toperform mathematical calculations, on a pixel-by-pixel basis, in orderto enhance and emphasize particular details in the X-ray image. When theimage processor 84 has the capability to perform such calculations, asdoes, e.g., the Matrox Image-LC processor board referenced previously,then such pixel-by-pixel calculations can be completed very rapidly.When the image processor 84 lacks this capability, as does, e.g., theMatrox IP-8, the calculations can still be performed by the SBC 70, butthey are not completed near as quickly.

[0084] Among the types of mathematical calculations that may beperformed on a pixel-by-pixel basis are various convolution techniques,accessible through commercially-available software, that modify thedisplayed image to produce a variety of effects. These effects include:(1) fine sharpening, which subtly increases the clarity of an image byenhancing high frequency components, making edges of objects appearsharper; (2) coarse sharpening, which is a variation of fine sharpening,but which produces a more dramatic noticeable sharpening; (3) smoothing,which reduces the “grainy” appearance of an image having excessive highfrequency noise; (4) horizontal edge detection, which suppresses (i.e.,turns black) all pixels in an image except for those which formhorizontal edges of objects in the image, thereby causing suchhorizontal edges to appear white, and making them stand out in highrelief; and (5) vertical edge detection, which does the same thing tovertical edges that the horizontal edge detect does to horizontal edges.

[0085] It is noted that other mathematical operations and functionscould also be used in addition to, or in lieu of, the above listedconvolution techniques in order to sharpen and enhance a given image.For example, multiple image arithmetic calculation functions, (i.e.,pixel-to-pixel Addition, Subtraction, Multiplication, Division, And, Or,Xor, etc.), Blob Analysis, Pattern Analysis, Fast Fourier Transforms,and other more extensive convolution techniques, could be performed.

[0086] Moreover, in addition to mathematical manipulation, the controlunit 16 permits a wide variety of display flexibility, which alsoenhances the desired details of an acquired image. For example, zoomingby factors of 2 and 4 are supported, allowing small details to bemagnified and viewed in greater detail. Panning and scrolling functionsare also available in conjunction with the zoom capability to allow auser to move about within the magnified image. A contrast stretchfunction, discussed in more detail below, is further provided whichinteractively allows the user to change the displayed contrast andbrightness of specific grayscale regions of the image. Such contraststretch function is particularly useful for increasing the brightnessand clarity of very dense objects.

[0087] An invert function is likewise provided within the control unit167 which changes the image from a black-to-white “positive” image intoa white-to-black “negative” image. Such function aids radiographers whoare more comfortable viewing images as they would appear, e.g., on X-rayfilm.

[0088] As indicated, the control unit 16 preferably operates in aWindows-based mode, thereby providing an operator of the system, oncethe system has been set up and turned on, the ability to select variousoptions related to the imaging task at hand. Such options are controlledby appropriate applications software that is stored on the unit'sinternal hard drive.

[0089] A flow diagram of the software control used within the unit 16 isillustrated in FIG. 7. As seen in FIG. 7, when power is first applied tothe unit, the computer is booted on and Microsoft Windows is loaded(block 90, FIG. 7). The electronics of the image processor 84 are theninitialized, power-on diagnostics are performed, and the single screendisplay capability is verified (block 92). Once initialized, a UserInterface Main Menu is drawn on the screen (block 94) using aconventional windows format.

[0090] The User Interface Main Menu screen allows the user to select oneof five options. A first option (block 96, FIG. 7) allows the user toget ready to acquire an image. Such option (as indicated at block 97)provides the user with an acquire menu that allows the user to controlthe X-ray image acquisition and exposure duration. Further detailsassociated with the selection of the “Acquire” option are presentedbelow.

[0091] A second option (block 98) provides the user with a “files” menu.The files menu allows the user to store and retrieve images in binaryformat to and from digital media (block 99), e.g., an internal harddrive, a floppy disk, or a removable hard drive.

[0092] A third option (block 100) provides the user with a “display”menu. The display menu allows the user to enhance details of thedisplayed image (block 101) by, e.g., zooming, contrast manipulation,grayscale inversion, and buffer changing.

[0093] A forth option (block 102) provides the user with a “modify”menu. The modify menu allows the user to mathematically enhance thedisplayed image (block 103) using convolution techniques. Suchmathematical enhancements include, at the present time, coarse and finesharpening, smoothing, and marking horizontal and vertical edgedetection.

[0094] A fifth option (block 104) provides the user with a “help” menu.The “help” menu provides the user with whatever information may behelpful to the user, e.g., a further description of the other options,the latest enhancements that have been included in the software, and/orany other information that helps the user debug any problems he/she maybe experiencing with the operation of the system 10.

[0095] A representation of the User Interface Main Menu is presented inFIG. 8A. This menu is displayed on the display screen 28. Note that theMain Menu appears as a conventional “window” for use within a Microsoftwindows environment. There is a menu bar 110 located across the top ofthe screen, and a column of icons 112 located on the right of thescreen. From this main Windows menu, the user can access the variousoptions provided by pull-down menus or icons associated with eachoption. The functions which can be activated by the icons are a subsetof the functions which can be accessed through the pull-down menus.

[0096] As with any Windows environment, selection and activation and/orinitialization of each of the various activities represented by thecorresponding icons or pull-down menu options is made using the arrowcursor displayed on the flat panel display, or by using keyboardselections consistent with the standard Windows applications. That is, afunction represented by an icon is activated, e.g., by simply moving thearrow cursor to the point within the appropriate icon using the mouse(or other pointer device) and pressing (or “clicking”) the left buttonon the mouse, or moving the arrow cursor to the named menu item on themenu bar and pressing the left mouse button. Alternatively, the “Alt”key may be pressed simultaneously with the first (or underlined) letterof the named menu item on the menu bar.

[0097] To illustrate, an X-ray image is acquired by moving the arrowcursor and pointing-and-clicking on the Acquire option on the menu bar110, or equivalent icon in the icon column 112. Such action causes theAcquire pull-down menu to be activated, as represented in FIG. 8B. TheAcquire pull-down menu lists three options, as shown in FIG. 8B,including “Grab”, “Exposure Time”, and “Exit”. An image acquisition isreferred to as a “grab” because it entails pulsing the X-ray source 12and “grabbing” the video data resulting therefrom which make up theradioscopic image.

[0098] Once the Grab option has been activated, a dialog box appears inthe center of the Display Panel as shown in FIG. 8C. This dialog boxserves as a safety feature, or software interlock, that warns theoperator that X-ray production will be initiated by the next step, andthat the X-ray beam area should be clear of all personnel.

[0099] As seen in FIG. 8C, two options are provided below the warning:(1) to produce X-rays and acquire an image, the user must use the mouseto point-and-click on the OK button; or (2) the grab request can becanceled by using the mouse to point-and-click on the Cancel button,which returns the user to the Acquire pull-down menu (FIG. 8B). When theuser selects the OK option, the X-ray source pulses immediately and animage forms on the display panel 28. This image is the radioscopic imagethat is created by having X-rays directed at and pass through the object22, as sensed by the imager 14, and processed by the circuitry withinthe control unit 16. Advantageously, at the completion of the Grabsequence, the system returns to the Acquire pull-down menu, and theacquired radioscopic image is displayed beneath the menu overlaygraphics.

[0100] As mentioned previously, there is an interlock key 24 located onthe control panel of the control unit 16, and another interlock key 26located on the X-ray source. These interlock keys are intended toenhance radiation safety. Both of these keys must be in place and turnedto the ON position in order for X-ray production to occur. If either ofthese keys is not in place and in the ON position, the X-ray source willnot fire, a call to the Grab function will time-out, and the system willreturn to the Acquire pull-down menu without creating a radioscopicimage.

[0101] Once an image has been acquired, the user may select other menubar or icon bar options depending on what is to be done next. If theacquired image is not quite right, e.g., due to under or over exposure,or the feature(s) of interest in the image are not properly oriented fordefinitive evaluation, another image may be acquired after appropriateadjustments are made to the image acquisition time. Such adjustments aremade using the Exposure option in the Acquisition pull-down menu, or byadjusting the X-ray source/target/imager geometry. If the quality of theimage just acquired is satisfactory, the image can be stored to harddisk or floppy disk using the options found in the File pull-down menu.Further, an acquired image can be visually manipulated using thefunctions found in the Enhance or Modify pull-down menus. For example,an image which has just been acquired will usually benefit from theSharp 1 or Sharp 2 enhancements presently offered as the first andsecond options, respectively, in the Modify menu. These edge sharpeningoptions use the image processor's capabilities to make the acquiredimage appear sharper than the original image. It is to be emphasized, ofcourse, that the use of such edge sharpening options are meant to beexemplary, not limiting.

[0102] One particular image enhancement feature of note is the ContrastStretch option available through the Display pull-down menu. TheContrast Stretch option of the Display menu is used to change thegrayscale level distribution of the displayed radioscopic image tofacilitate visualization and evaluation by the operator of features ofparticular interest. This Contrast Stretch option is a particularlyvaluable option for the present invention due to the large range ofgrayscale resolution that is available with the display 28. As indicatedpreviously, the display 28 preferably includes the capability ofproviding 256 different levels or shades of gray, ranging from black towhite, within the displayed image. For example, a pure black pixel isrepresented by a gray scale of 0, while a pure white pixel isrepresented by a gray scale of 255.

[0103] A mapping function is used to map a given intensity (e.g., numberof X-ray pulses received at a given pixel site) to a given grayscalevalue. Thus, for example, a pixel value of 0 (black) means that noradiation was sensed at the given pixel, whereas a pixel value of 255(white) indicates that a maximum radiation level was sensed at the pixelsite.

[0104] In the preferred embodiment, the mapping function that relatesthe sensed intensity of a given pixel site to a specified grayscalevalue is linear. It is to be emphasized, however, that the mappingfunction need not be linear, but can be any value. Performing a ContrastStretch function changes the “slope” and “offset” of the mappingfunction. Slope and offset are best understood with reference to FIG. 9.

[0105]FIG. 9 depicts a graph that illustrates representative mappingfunctions that may be used to map the number of sensed pulses at a givenpixel site (vertical axis) to a grayscale value (horizontal axis). Thus,for example, the dashed line 130 represents a linear mapping functionwith no offset and with a slope of n/255, where n represents a specifiedmaximum number of pulses that can be sensed. The solid line 132 in FIG.9 represents a mapping function with no offset, and having a slope ofn/m where m is about ½ of 255. The slope of line 132 is thus about twicethat of the line 130. Solid line 134 has a slope that is about the sameas that of line 132, but with an “offset” of p, where p is an integerthat is about ⅖ of m. The offset thus defines the location within thepixel value range where the linear (or nonlinear) ramp begins. Thedashed line 136, for example, defines a ramp that has the same offset pas the line 134, but is not linear. Rather, the line 136 has a general“S” shape, and thus has a varying slope that is the steepest in the midrange of the number of sensed pulses. The dashed-dotted line 138 has anoffset of r and a slope that is the steepest of all the lines shown inFIG. 9.

[0106] The present invention thus allows the offset and slope of thedisplayed image to be readily defined using, e.g., the Contrast Stretchfunction, thereby allowing the quality of the displayed image to beimproved. In its present configuration, the Contrast Stretch option actsonly on the output to the display panel 28. When images are stored todisk and subsequently retrieved, they will not be stretched as displayedprior to archiving. That is, saving an image to hard or floppy diskstores the data in the display memory buffer, but not the video outputparameters. Nonetheless, storing and saving the video output parameters,as well as the image, is something that could be done by those of skillin the art if needed and/or desired.

[0107] The image enhancement tools described herein are realized usingcommercially available imaging application development software. Suchsoftware may be obtained, e.g., from Matrox Electronic Systems, Ltd., ofQuebec, Canada. Matrox provides, e.g., numerous software programs,including a Windows Utility, that allows a user to load, grab, create,duplicate, save, transmit, display, overlay, and/or process digitalimages. All of the enhancement features, such as course and finesharpening, smoothing, horizontal and vertical edge detection, grayscaleinversion, contrast stretching, zooming, and buffer changing, aresupported by software programs and/or hardware that are commerciallyavailable from companies such as Matrox, or other companies like Matrox,e.g., Data Translation, Inc., 100 Locke Drive, Marlboro, Mass.01752-1192.

[0108] As described above, it is thus seen that the present inventionprovides a high-resolution, solid-state imaging system that utilizeson-chip light integration, thereby eliminating the need for intensifyingelectro-optic components, and wherein the system is based on apersonal-computer controller that facilitates the acquiring, displaying,storing, enhancement, and/or transmitting of a digital image obtainedwith the system. Advantageously, such system is self-contained,lightweight and portable, and can easily be taken on-site to inspectwhatever objects need to be examined without having to move suchobjects. Once an image is acquired, the image can be immediately sent asdigital data over a modem, provided as part of the system, or stored ona floppy disk, or removable hard disk, to facilitate its transfer to anoff-site location where the image can be faithfully reproduced forfurther analysis by off-site experts.

[0109] An additional preferred embodiment describes as follows, providesfor the propagation of visible light from the X-ray converting screen 42outwardly from each point 154 impinged by X-ray radiation 152, so as toincrease the fraction of light 154 directed towards the CCD cameraobjective lens 46, while simultaneously reducing the amount of scatteredvisible light.

[0110]FIG. 10 illustrates the basic emission of light from the diffusephosphor screen 42 without transmissive films as is employed in theembodiment of FIG. 3A discussed above in the mirror folded approach usedwith the described embodiments. Herein, the phosphor screen 42 isconverts the impinging X-ray radiation 152 to visible light such thateach point 154 impinged on the phosphor screen 154 by X-ray radiation152 scintillates visible light emissions 156 diverging from the phosphorscreen 42.

[0111] The light emission in FIG. 10 show an incident 180 degree cone ofillumination, from which diverging emissions 156 may reflect off themetal housing 40. Light emissions 158 may then cause scattered light160, 162 which may result in degraded contrast and image resolution.With the wide cone of illumination of FIG. 11, only a fraction ofgenerated light 164 is collected at the lens 46 of the CCD camera.Generally, one tries to make the walls 40 of the system 150 physicallydistant from the beam and coat wall 40 surfaces with non-reflectivematerial. However, with the mirror folded optical systems used herein,such approaches are complicated to employ. Moreover, if one wants torestrict the depth of the optical system by using a mirror angle of 45degrees or greater, the problem of limiting the light emitted 156 andkeeping light 158 from reflecting back onto the diffuse phosphor surfacewhere they may now bounce back into the collected beam 162 is verydifficult.

[0112] To this end, the restriction and focusing of light directly onthe surface of the phosphor screen 42 using thin light directing filmsor structures presents an attractive approach to improve contrast andbrightness of radiographic systems which use lenses coupled with X-rayconversion screens. Depending whether the light directing material usessimple masking of emission angles or employs the refraction of an arrayof lenslets or linear micro-prisms, the method can effectivelyconcentrate the emission angle of the normal lambertian pattern andredirect the centroid of that angular distribution toward the enter ofthe collecting lens. In effect, the method trades off an increase inbrightness and reduction in off axis emission for the spatialquantification of the totality of light emitted.

[0113] The improved system 200 of FIG. 11 represents a radiographicsystem utilizing transmissive films as an emission modification devicefor generally focusing the diverging visible light as a restricted coneof illumination. Herein, the radiographic system 200 utilizes atransmissive film emission modification device or lens 202 such as amicrolens film. The improved X-ray converter screen 202 includes asubstrate 206 converting impinging X-ray 152 radiation to visible light,each point 154 impinged on the substrate 206 thus scintillates visiblelight emissions. An image sensor CCD camera is configured to sense thevisible light using a first lens 210 operable for spatially sensing thevisible light within a collection cone 220 directed outwardly. A secondlens 204 is provided as a transmissive film through which the visiblelight emitted from the substrate 206 is transmitted. The second lens 204is positioned in an optical path between the first lens 210 and thesubstrate 206 for generally focusing the diverging visible light as arestricted cone of illumination 208 propagating outwardly from eachpoint 154 impinged to increase the fraction of light directed into thecollection cone 220 of the first lens 210 while reducing the amount ofscattered visible light from said screen.

[0114] The lens 210 is provided as an aspherical lens for using a largeaperture without developing aberrations and loss of sharpness; an F/0.8aperture is used with minimal loss of sharpness. The lens 210 used inthe described embodiments is made by COMPTAR, Chugai Boyeki (America)Corp., Japan, which has provided satisfactory low light opticalperformance with a wide aperture, whereas most optical systems tend tosuffer serious spherical aberration when wide apertures are employed.

[0115]FIG. 12 shows linear prismatic lens 204 superposed with an X-rayconverting screen as is employed in the radiographic system of FIG. 11.Depending whether the light directing material uses simple masking ofemission angles or employs the refractive of an array of lenslets orlinear microprisms, the method can effectively concentrate the emissionangle of the normal lambertian pattern and redirect the centroid of thatangular distribution toward the enter of the collecting lens. A discretesmall optical gap is provided between the phosphor and the optical filmto allow the light rays to be refracted in a direction more nearlynormal to the emission plane. The screen 204 is then vacuum sealed withthe transmissive film 204 with the optical gap provided between saidphosphor screen and the transmissive film.

[0116] As shown in FIG. 12, the enhanced converter screen can beeffected using linear structures along a single axis or can be effectedusing crossed linear structures and one or two dimensional structures toprovide enhancement of the optical emission properties in two directions(FIG. 16). Examples of films which can produce the desired effects arecurrently produced by 3M Corporation for the purpose of controllingangle of view for computer screens and traffic lights. The 3M materialsare referred to as a family of transmissive films known as BrightnessEnhancement Film (BEF), and Transmissive Right Angle Film (TRAF). In thedescribed embodiment of FIG. 12, BEF II film from 3M Corp. was used.Herein, limiting the angle of emission and transmitted intensity usingchevron-like baffles on the screens surface, refocus it with a sheet oftiny microlens or one or more linear microprism structure which collecta large fraction of the light emitted below their area. Typically theoptically active structures have a focal point is very near the screen'ssurface which allow the light to be highly focused or by proper choiceof orientation can also redirect an already restricted emission toincline its center more into the collection cone and away from any othersurfaces within the enclosure.

[0117] In addition to the use of the array of micro-lens covering aconventional X-ray to light of FIG. 12A, an alternate embodiment employsthe use of a layer of sprayed micro-spheres lenses. As shown in FIG.12B, substantial improvements in brightness and optical scatterrejection also may be achieved in the alternate embodiment with a layerof sprayed micro-spheres of optical index, n_(h) for concentrating theemission light core from converter screen used in an X ray imager. Theimprovements in performance were achieved because the effect of themicro-lens was to reduce the size of the emission cone of light from thescreen and thus better match the acceptance cone of the observing lens.However, there were several practical difficulties that are inherentwith such micro-lens arrays that are overcome in the presently describedalternate embodiment. They are generally not available with very highoptical index materials which reduces their focusing strength and oftenare on substrates which are not well matched in thickness to the optimumoptical collection geometry. In almost all cases, these lens arrays areexpensive and the cost increases non-linearly with overall area.

[0118] In implementations of this micro-lens approach, one is employinga form of non-imaging optics in which the function of each lens elementis to brighten the output of the area beneath it by concentrating theoutgoing light cone. The trade off made in this optical gain is thecomplete loss of detail within the individual micro-lens area. Thereforethe image becomes pixilated into elements the size of each lensletelement. If the lens have a very high optical index, they can be made invery small radii of curvature and still allow the light to be wellconcentrated through their volume. Typical thermoplastics used formaking replica micro-lens arrays generally are very limited in range ofoptical index. Certain glasses and other clear crystals may have muchhigher indices and therefore may be more effective as focusing elements.

[0119] In the current implementation of this work, it is, therefore,suggested that an equivalent lens array may be formed by successivespray or coating of a conventional X-ray converter screen with a binderof some intermediate optical index, n_(h). This initial binder layer isthen over-sprayed with a very fine and even layer of solid micro spheresof even higher index, n_(n). The result is equivalent to the array oflenslets but is easier to fabricate and covers any given sized screenwith no additional difficulties. As shown in FIG. 12B, light from thescreen, which would normally be Lambertian or at least be emitted in avery wide cone, is concentrated by the presence of the sprayed onmicro-lens. The intermediate binder layer may be optimized in thicknessand optical index so that the focal point of the lens elements would bevery nearly equal to the distance the lens layer was placed above thescreen. In practice, if n_(h), is very high, this can be nearly incontact with the screen making the binder layer very thin anduncritical. Micro-spheres with very high optical index are often used toenhance paints and lacquers and are commercially available. Moreover,modern spray techniques are available to spray such micro-spheres in avery fine binder with low inherent solids content so that the finalthickness of that layer can be well controlled. This process issignificantly easier and less expensive to apply and would be applicableto a wider variety of converter screens and imaging situations.

[0120]FIG. 13 illustrates transmissive film 214 having a multiplicity ofslats 216 which restrict the transmission of light to emissions 218directed by the orientation of the slats with a venetian blind like filmwherein an angle restricting baffle is formed from a microscopicdistribution of dark slats formed within the film. This is a simplephysical restriction of the beam and the angle of emission is limited bythe average angle of the slats to the normal, the ratio of slat width toslat. pitch and the original distribution of the light from the from thesource. The major advantage of this device is that it need not bedirectly in contact with the phosphor screen to work and that twodevices placed in tandem with a 90 degree rotation produce a squareemission cone. Since all present films are uniform, this is really acone of near infinite length since the light comes out at one angle witha rapid fall of in either direction. The limitation of the method isthat the light comes off in near parallel rays rather than being focusedinto the finite cone of the lens and that it throws away all rays thatare not initially moving in the proper direction. This limitation can bemitigated by curving the film containing the chevrons so that the lightis allowed to come out in a cone focused onto the lens or other opticalsensor.

[0121]FIG. 14 is a radiographic system showing microlens film focusingthe diverging visible light as restricted cones of illuminationpropagating towards the collection cone of the objective lens 210. Theoptimal implementation of these films corresponds to a spatially varyingfilm 222 which focuses and bends the light along a one dimensional conefollowed by a second layer which does the same for the second axis. Sucha film is not currently available but can be approximated by usingsections of the fixed angle films and orienting the angles to favor thecone of collection along both axis. A composite structure may be devisedfrom either oriented lenslets of combinations of varying anglemicroprism arrays which cause the light to be contained within a smalleremission cone, move the central axis of the cone off the perpendicularand toward the lends and provide a smooth reflective surface for anylight that does happen to bounce back toward the screen. These films arebuilt in the form of series of repeated long prisms impressed onto athin resin film. The prisms are adjusted so that any light originatingfrom below is diverted selectively depending on its angle of incidence.Thus, the light intensifying screens can collect light emitted from neartheir optical focal length and compress the incident 180 degree coneinto an out going cone of 30 to 40 degrees in one dimension. Since thesource of the light is very near the prism, the resolution is againlimited to the pitch of the prism array. Depending on the angle of theprism, the cone can be made narrower and brighter or wider and lessintense. Using two films at 90 degrees again provide two dimensionalfocusing of light but at some loss of resolution since the second gridmay not be properly spaced. from the source of the original light orsimply because its capture angle now includes a larger spot on thesurface of the phosphor. Alternative configurations of these filmsprovide prisms with non-symmetric angles 222 which can not only focusthe emitted light but also cause its centroid to be bent along aspecific angle 224 into the collection cone of the lens 210.

[0122]FIG. 15 depicts the operation of transmissive film in the form ofmultiple corrective microlenses 226 for directing light emissions.Modification of focusing schemes to provide a conical convergence of theorientation of the light beams to further enhance the effectiveness ofthe light control and to flatten the intensity response 228 when using awide angle collection lens on the sensor camera. A system using acombination of these films, directly adhered to the phosphor is improvedin several ways. First, only light moving in the general direction ofthe lens is favored with other rays being attenuated, second, light thatdoes escape the collection cone and hits a flat surface returns to hit asmooth surface rather than a diffuse one. The reflection angle is welldefined and not likely to be recaptured within the collection cone.

[0123]FIG. 16 shows a prismatic film 230 having corrective microlensesor prisms in two dimensions, e.g., using crossed prismatic films for a2-dimensional focus, or using molded lenslets for 2-dimensionalfocusing. Thus, the operation of transmissive film in the form ofmultiple corrective microlenses for directing light emissions.

[0124] While the invention herein disclosed has been described by meansof specific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

What is claimed is:
 1. An X-ray converter screen, comprising: asubstrate for converting impinging X-ray radiation to visible light,each point impinged on said substrate by X-ray radiation scintillatingvisible light emissions diverging from said substrate; and an emissionmodification layer comprising micro-spheres having an optical indexthrough which the visible light emitted from said substrate istransmitted, said emission modification layer generally limiting thediverging visible light to a restricted cone of illumination propagatingoutwardly from each point impinged on said substrate by the X-rayradiation.
 2. An X-ray converter screen as recited in claim 1, whereinsaid emission modification layer enhances light collection from thevisible light converted by said substrate to improve the opticalcollection efficiency.
 3. An X-ray converter screen as recited in claim1, wherein said emission modification layer comprises a layer of saidmicro-spheres supported with a binder layer affixed to said substrate.4. An X-ray converter screen as recited in claim 3, wherein saidemission modification layer is sprayed on said substrate.
 5. An X-rayconverter screen as recited in claim 3, wherein said substrate comprisesa phosphor screen made out of deposited crystals of a salt that givesoff visible light when impinged upon by X-rays.
 6. An X-ray converterscreen as recited in claim 3, wherein said emission modification layercomprises a transmissive film for refracting the visible lightpropagating therethrough.
 7. A radiographic system, comprising: an X-rayconverter screen for converting impinging X-ray radiation to visiblelight, each point impinged on said screen by X-ray radiationscintillating visible light emissions diverging from said screen; animage sensor configured to sense the visible light from said screen; afirst lens operable with said image sensor for spatially sensing thevisible light within a collection cone directed outwardly from saidimage sensor; and a second lens through which the visible light emittedfrom said screen is transmitted, said second lens comprisesmicro-spheres of an optical index for concentrating the visible lightsupported with a binder layer being positioned in an optical pathbetween said first lens and said screen for generally focusing thediverging visible light as a restricted cone of illumination propagatingoutwardly from each point impinged on said screen to increase thefraction of light directed into the collection cone of said first lensand reducing the amount of scattered visible light from said screen. 8.A system as recited in claim 7, wherein said second lens comprises asprayed layer of said micro-spheres for refracting the visible lightpropagating therethrough.
 9. A system as recited in claim 8, whereinsaid sprayed layer comprises a transmissive film surface structurehaving a multiplicity of micro-spheres for focusing the visible lightemitted from said screen.
 10. A method of converting X-ray radiation tovisible light, comprising the steps of: providing a phosphor screen forconverting impinging X-ray radiation to visible light, each pointimpinged on the phosphor screen by X-ray radiation scintillating visiblelight emissions diverging from the phosphor screen; and superposing thephosphor screen with a sprayed layer of micro-spheres for modifying thetransmission of visible light emitted from the phosphor screen togenerally limit the diverging visible light to a restricted cone ofillumination propagating outwardly from each point impinged on thephosphor screen by the X-ray radiation.
 11. A method as recited in claim10, wherein said superposing step comprises the step of spraying on abrightness enhancement transmissive film.
 12. A method as recited inclaim 10, comprising the step of vacuum sealing the phosphor screen withthe transmissive film.
 13. A method as recited in claim 10, comprisingthe step of providing an optical gap between the phosphor screen and thetransmissive film.